1. Field of the Invention
This invention relates to an optical transmission tube comprising a tubular transparent cladding and a transparent core having a higher index of refraction than the cladding and a method for preparing the same. More particularly, it relates to an optical transmission tube allowing directional light emergence from one side or outer surface area of the cladding. It also relates to a linear illuminant system having improved water resistance, improved environmental resistance and a low power consumption for driving.
2. Prior Art
Since optical transmission tubes comprising a tubular cladding and a core in the cladding having a higher index of refraction than the cladding are generally designed so as to transmit as much light as possible from one end to the other end thereof, only a low luminance is generally available near the side surface of the tube. One possible measure for increasing the luminance at the side surface of an optical transmission tube is by corrugating the cladding inner surface for scattering light. This measure is difficult to apply to the method for producing an optical transmission tube by filling a tubular cladding with a core-forming polymerizable monomer liquid and pressurizing the liquid for causing the monomer to polymerize because the cladding becomes likely to rupture.
It may also be envisaged to disperse scattering particles in the core for increasing the luminance at the side surface of an optical transmission tube. It may occur to those skilled in the art to disperse scattering particles in a monomer liquid and then polymerize and solidify the monomer. However, there has never been available a method of adding scattering particles to a monomeric liquid and polymerizing the liquid in a controlled manner such that the scattering particles are distributed in a limited area, that is, to form a reflecting layer, at the end of polymerization.
Known illuminant devices capable of providing linear light emission over a length of several meters include neon tubes and fluorescent tubes. The neon tubes and fluorescent tubes require high voltages, with the risk of electric shocks and leakage. They cannot be used in water and at places where rain or snow reaches. Since the tubes are formed of glass, they cannot be used at places where failure of glass tubes by physical collision of people or vehicles is expectable.
Where the neon tubes and fluorescent tubes are used in a bent form, the glass tubes must be worked to the desired curvature, which requires skilled workers and hence, leads to an increased cost. The power consumption of neon tubes and fluorescent tubes is as high as several tens of watts per meter. For a long term of operation, they must be installed where a commercial power supply is available.
To solve these problems, optical transmission tubes in the form of a flexible tube filled with a transparent core liquid or flexible transparent polymer and strands of plastic optical fibers have been proposed. The system includes a light source and an optical transmission tube which receives light from the light source at one end thereof. The optical transmission tube is designed such that light may emerge from a side surface area of the tube over a length of several tens of meters. Since the light source can be separated from the light emerging area, this system can be used in water, outdoor or even in an environment with the risk of explosion. The system is free of the risk of breakage, eliminates complex cumbersome working such as glass working, and is readily applied at a necessary site.
These optical transmission tubes provide light emergence over a length of several tens of meters. Since the light emergent efficacy at the side surface is low, a high power light source of about 50 to 250 W is required in order to provide an increased luminance. When such an optical transmission tube is used in water, outdoor or in an environment with the risk of explosion for the purpose of providing side surface light emergence, a means for protecting the light source is necessary. As a consequence, the light source is increased in size and its accommodation is significantly limited.